1. Field of the Invention
The present invention generally relates to a wireless talking apparatus in which transmission of signal is performed by utilizing an antenna and simultaneous talking can be performed, and more particularly to a wireless talking apparatus in which not only talking can be performed in a full-duplex communication mode when a main communication device and a subsidiary communication device are used in one-to-one correspondency but also if further one or more subsidiary communication devices are prepared, simultaneous talking can be performed also between or among the subsidiary communication devices.
2. Description of the Prior Art
Conventionally, there have been proposed various kinds of wireless talking apparatus for communication between separated positions in which not only signal transmission is performed by utilizing an antenna but also simultaneous talking can be performed between two communication devices by utilizing two carrier waves of different frequencies in a specific frequency band assigned for the communication. For example, as shown in FIG. 1, the conventional wireless talking apparatus of this kind is provided with a first communication device 11 and a second communication device 12. The first communication device 11 is provided with a transmitter 13 for transmitting a carrier wave of a frequency f.sub.1. The second communication device 12 is provided with a transmitter 15 for transmitting a carrier wave of a frequency f.sub.2 and a receiver 16 for receiving the carrier wave of the frequency f.sub.1. The transmitter 13 is provided with a microphone 17 for receiving a voice of an operator A to produce a voice signal, a transmitter circuit 18 for transmitting the voice signal from the microphone 17, an antenna 19 for transmitting an output signal from the transmitter circuit 18 to the second communication device 12, and an antenna matching and distributing circuit 21 for automatically switching a signal path such that the signal from the transmitter circuit 18 is transmitted to the antenna 19 and a signal from the second communication device 12 received by the antenna 19 is applied to the receiver 14. The receiver 14 is provided with a receiver circuit 22 for receiving the voice signal from the second communication device 12 and a speaker 23 for converting the voice signal received by the receiver circuit 22 into a voice sound. The antenna 19 and the matching and distributing circuit 21 are commonly used by the transmitter 13 and the receiver 14. Similarly to the transmitter 13, the transmitter 15 in the second communication device 12 is provided with a microphone 24 for receiving a voice of another operator B, a transmitter circuit 25, an antenna 26, and an antenna matching and distributing circuit 27. Similarly to the receiver 14, the receiver 16 in the second communication device 12 is provided with a receiver circuit 28, a speaker 29, an antenna 26 commonly used for the transmitter 15, and an antenna matching and distributing circuit 27.
When the operators A and B carry the first and second communication devices 11 and 12 respectively, the operator A can hear the voice of the operator B through a radio wave formed by modulating the carrier wave of the frequency f.sub.2 with the voice signal, while the operator B can hear the voice of the operator A through a radio wave formed by modulating the carrier wave of the frequency f.sub.1 with the voice signal. Since the frequencies f.sub.1 and f.sub.2 of the respective carrier waves are different from each other, the radio waves do not interfere with each other and the operator A and B can talk while hearing the other operator's voice in the same way as ordinary conversation. However, for example, even if a further additional second communication device 31 which is quite the same as the second communication device 12 is prepared and carried by a third operator C, talking between the operators B and C is quite impossible. If the transmission by the additional second communication device 31 is turned off so that the radio wave thereof does not interfere, it is possible to perform simultaneous talking between the operators A and B in the manner as described above. However, the operator C can not hear the voice of the operator B but can hear only the voice of the operator A.
In order to improve the device in the disadvantage as described above, there has been proposed a multi-talking wireless communication apparatus in which a repeater is provided so as to perform simultaneous talking among a plurality of communication devices. Referring to FIG. 2, such a communication apparatus will be described hereinafter.
In the drawing there are provided three communication devices 32, 33, and 34, and a repeater 35 for enabling mutual talking thereamong. The communication device 32 is provided with a transmitter T.sub.1 for transmitting a carrier wave of a frequency f.sub.1, the communication device 33 is provided with a transmitter T.sub.2 for transmitting a carrier wave of a frequency f.sub.2, and the communication device 34 is provided with a transmitter T.sub.3 for transmitting a carrier wave of a frequency f.sub.3.
The communication devices 32, 33, and 34 are also provided with three receivers R.sub.0 each receiving a carrier wave of a frequency f.sub.0. The repeater 35 is provided with receiving repeaters R.sub.1, R.sub.2 and R.sub.3 which correspond to the transmitters in number, and a transmitter T.sub.0 for mixing the received signals from these repeaters and for transmitting a carrier wave of a frequency f.sub.0. Since the respective frequencies of the transmitters T.sub.1, T.sub.2, and T.sub.3 and the transmitter T.sub.0 are different from each other, they do not interfere with each other and, therefore, the simultaneous talking can be mutually performed through the repeater 35 among the operators A, B and C who carry the communication devices 32, 33, and 34 respectively, similarly to an ordinary conversation mode.
In the thus arranged wireless communication apparatus for multi-talking, however, the repeaters as described above are always necessary, so that the apparatus is inconvenient when it is used in one-to-one correspondency for performing the simultaneous talking. Since the used receiving repeaters are required to meet the number of the provided communication devices, the number of the provided communication devices must be set in advance, so that the number of the communication devices can not be simply increased. Further, the repeater 35 mixes the received signals from the transmitters T.sub.1, T.sub.2, and T.sub.3 and the transmitter T.sub.0 modulates the carrier wave with the mixed signal and transmits the modulated carrier wave. Accordingly, the assignment of modulation rate for the respective received signals from the receiving repeaters R.sub.1, R.sub.2 and R.sub.3 becomes one-third, and in the case where ten communication devices are provided, the assignment of the modulation rate of the same becomes one-tenth, so that SN (signal to noise) ratio becomes considerably worse and therefore the communication devices can not be used practically.